- Brake Pedal Mechanical Advantage
- it is how far the brake pedal travels to how far the brake pads move using leverage to increase the amount of force to master cylinder brake pedal is a second class lever ratio of the distance to the pivot point.
- The Hydraulic Braking System
- The brake pedal force is transfered to the hydraulic system, where the force is transfered through the lines and hoses to each wheels caliper or wheel cylinder
- Pascal’s Law
- When force is applied to a confined liquid the pressure is transmited equal and undiminished
- force= pressure x area
- Master Cylinder Reservoirs
- hold brake fluid, the capacity is great enough to allow for the breaks to become completely worn out and still have enough reserve for safe operation
- Master Cylinder Reservoir Diaphragm
- A brake master cylinder reservoir diaphragm has a vent slit therein to operate as a vent valve to equalize air pressure when a pressure differential is impressed across the diaphragm as the brake fluid level in the reservoir changes.
- Master Cylinder Operation
- When you press the brake pedal, it pushes on the primary piston through a linkage. Pressure builds in the cylinder and lines as the brake pedal is depressed further. The pressure between the primary and secondary piston forces the secondary piston to pressureize the fluid in its circuit. If the brakes are operating properly, the pressure will be the same in both circuits.
- Bypass Port
- also called the inlet port, filler port, or breather port. allows air to be released.
- Compensating Port
- a small hole in the wall of a tandem master cylinder which connects the brake fluid reservoir to the pressure chamber
- Master Cyl. At Rest Position
- The primary sealing cups are between the compensating port hole and the inlet port hole. In this position the fluid is free to expand in the calipers, wheel cylinders, and brake lines up into the reservoir through the vent port (compensation port) if the temperature rises and fluid expands.If the fluid was trapped, the pressure of the brake fluid would increase with temperature, causing the brakes to self apply.
- Master Cyl. Applied Position
- When the brake pedal is depressed, the pedal linkage forces the pushrod and primary piston down the bore of the master cylinder. As the piston moves forward, the primary sealing cup covers and blocks off the vent port. Hydraulic pressure builds in front of the primary seal as the pushrod moves forward. The back of the piston is kept filled through the replenishing port. This stops any suction from forming behind the piston. The secondary piston is moved forward as pressure is exerted by the primary piston. If, for any reason, such as a leak, the primary piston cannot build pressure, a mechanical link on the front of the primary piston will touch the secondary piston and move it forward, as the primary piston is pushed forward by the pushrod and brake pedal.
- Master Cyl. Released Position
- the point at which the brake pedal and the pushrod return from the fully applied postiton back to the at rest position.
- Residual Check Valves
- maintains a small amount of presure in the lines to prevent air dirt or contaminents from entering the system
- Dual Split Master Cylinders
- uses two separate pressure-building sections. on section operates the front brakes and ther other section operates the rear brakes on vehicles equipped with a front/rear-split system.
- Diagonal Split Master Cylinders -
- Type of master cylinder where braking is proportioned to opposite diagonal corners of the vehicle - FR and RL, and FL and RR (and vice versa)
- Quick Take-Up Master Cylinders- The quick take-up master cylinder includes a quick take-up valve which assists the flow of fluid to the primary brakes to “take up” the extra clearance of the front brake calipers.
- Diagnosing and Troubleshooting Master Cylinders http://www.ehow.com/how_5006479_troubleshoot-brake-master-cylinders.html
- Spongy Pedal
- a symtom when the brake pedal is not as firm. Can be caused by air in the brake system
- Low Pedal
- Usually caused by one side of the dual port hydraulic syetem not working.
- Or the out of adjustment of drum brakes allowing to much pedal travel.
- Also can be casue by air in the brake lines
- Sinking Pedal
- When you go to apply the brakes and they sink to the floor, happens when you have a fluid leak or defictive master.
- Disassembly of Master Cylinder
- step 1 Remove master cylinder from the vehicle, being careful not to drip brake fluid onto painted surface. Dispose of all old brake fluid and clean the outside of master cylinder.
- step 2 Remove the reservoir if possible.
- step 3 Remove the retaining bolt that holds the secondary piston assembly in the bore.
- step 4 Depress the primary piston with a blunt tool.
- step 5 Remove the snap ring and slowly release the pressure on the depressing tool. Spring pressure should push primary piston out of the cylinder bore.
- step 6 Remove the master cylinder from the vise and tap the open end of the bore against the top of a workbench to force the secondary piston out of the bore. If necessary, use compressed air in the outlet to force the piston out.
- Inspection and Reassembly of Master Cylinder
- Inspection
- 1. Check the brake fluid for proper level and condition.
- 2. Check that the vent holes in the reservoir cover are open and clean.
- 3. Check that the reservoir cover diaphragm is not torn or enlarged.
- 4. Check for any external leaks at the lines or at the pushrod area.
- Reassembly
- Step 1 Install the secondary piston assembly into the bore, spring end first.
- Step 2 Install the primary piston assembly , spring end first.
- Step 3 Depress the primary piston and install the snap ring.
- Step 4 Install the retaining bolt.
- Step 5 Reinstall the plastic reservoir.
- Step 6 Bench bleed the master cylinder.
- Inspection
- Pressure Differential Switch
- a pressure differential switch is used on all vehicles built after 1967 with dual master cylinders to warn the driver of a loss of pressure in one of the two seperate systems by lighting the dashboard red brake warning indicator lamp.
- Brake Fluid Level Sensor Switch
- this is located in the master cylinder reservoir. this sensor will light up the red brake warning lamp on the dash if low brake fluid level is detected. two sommon types are float-type or a magnetic reed switch.
- Diagnosing a Red “Brake” Dash Warning Lamp
- Lights whenever a hydraulic system failure occurs
- For step in diagnosing is to make sure light works, by turning the key on and if the light illuminates for a second then shuts off.
- Proportioning Valve
- limits hydcraulic pressure to the rear brakes improving brake balance during hard stops
- located inbetween the naster cylinder abd the rear wheels
- Height Sensing Proportioning Valves
- valve that varies the amount of pressure that can be sent to the rear brakes depending on the height of the rear suspension. height of the rear suspension is determined by the load in the vehicle
- Metering Valve
- In an automotive hydraulic braking system, a valve that momentarily delays application of the front disk brakes until the rear drum brakes begin to act.
- Metering Valve Diagnosis and Testing
- The most accurate way of testing is to use pressure gauges. Install two guages, one in the pressure line coming from the master cylinder and the other in the outlet line leading to the front brakes. When depressing the break pedal, the gauges should read the same until about 3-30 psi when the metering valve shuts, thereby delaying the opperation of the front breaks. The master cylinder outlet gauge should show an increace in pressure as the break pedal is depressed further. Once 70-300 psi is reached, the guage showing pressure to the front breaks should match the pressure from the master cylinder. If the pressure doesnt match these ranges, then the metering valve should be replaced.
- Brake Lines
- strong, high pressure, double wall steel lines that carry brake fluid throught the system
- Double Lap Flares Double Lap Flaring offers additional strength for tube ends that are subjected to more stress and fatigue. The joint is designed so that the inside surface of the flare has a larger diameter so it does not interfere with flow characteristics of the system. Double lap flaring can be formed in the same shapes and meets the same specifications as the Single Flare.
- ISO Flares
- Used on metric lines
- also called bubble flare
- used on most modern vehicle
- flare has to be proper size to seal
- Coiled Brake Line
- steel brake lines are often coiled. the purpose of the coils is to allow movement between the brake components without stress that could lead to metal fatigue and brake line breakage.
- Armored Brake Line
- A brake line with a steel coil wrap around it. Used in vehicles where there is a possiblity of the brake line being damaged by rocks or debris. If an armored brake line is damaged, it should always be replaced by armored brake line sections.
- J-45505 Brake Line Flaring Kit - required by GM to make all brke line repairs, the J-45505 contains all of the tools necessary to cut, strip and flare brake pipe.
- Flexible Brake Hose
- A flexible portion of the otherwise rigid metal brake line is needed to allow the front wheels of the vehicle to move freely as the vehicle is steered and to allow the up-and-down motion at the rear wheels. These flexible brake hoses attach the rigid, metal brake line to the calipers at the four wheels.
- Bleeding Procedure
- manual bleeding, pressure bleeding, vacuum bleeding, and gravity bleeding are some of the different bleeding procedures. The reason you would bleed the brakes is if there is air in the system.
- Bleeder Valve Loosening Tips
- Hit and tap method- tap the bleeder lightly with a steel hammer to break the taper. then use i six point wrench and tap the wrench clockwise first then counter clockwise to loosen.
- Air punch method- use an air punch instead of a hammer. then follow the hit and tap method.
- Heat and tap method- heat the bleeder valve to help loosen. again turn clockwise before loosening. However all internal rubber parts must be replaced in this method due to the exposure of heat.
- Wax method- Heat the bleeder valve. then apply wax to the heated valeve and allow the melted wax to flow into the threads of the screw. let cool so wax hardens then turn clockwise, then counter clockwise to loosen. again all internal rubber parts must be replaced.
- Bleeding Sequence
- Right rear, Left rear, Right front, Left front
- Manual Bleeding
- Pressure BleedingStep 1 Consult manufacturer's instructions and fill the pressure bleeder with the proper type of brake fluid.Step 2 Make sure bleeder is properly sealed and fluid supply valve is closed then use compressed air to pressurize the bleeder to 30 psi is read on the bleeder gauge.Step 3 If vehicle is equipped with a metering valve, override it with the appropriate tool. Step 4 Clean the top of the master cylinder. then remove the master cylinder cover and clean around the gasket surface. Do not allow dirt to follow into reservoir.Step 5 Fill reservoir about half full with new brake fluid, then install the proper pressure bleeder adapter on the master cylinder.Step 6 Connect the pressure bleeder fluid supply hose to the adapter, making sure the hose fitting is secured.Step 7 Open the fluid supply valve on the pressure bleeder to allow pressurized brake fluid into the system. Check for fluid leaks that can damage the vehicle finish.Step 8 Slip a plastic hose over the bleeder screw of the first wheel cylinder or caliper to be bled.Step 9 Open bleeder screw approximately one-half turn, and let fluid run until air bubbles no longer emerge from the tube. Close the bleeder screw.Step 10 Transfer the plastic hose to the bleeder screw of thew next wheel cylinder or caliper in the bleeding sequence, and repeat steps 8 and 9. Continue around vehicle in the specified order until all have been bled.Step 11 Remove metering valve override tool.Step 12 Close fluid supply valve on pressure bleeder.Step 13 Wrap the end of the fluid supply hose in a shop towel, and disconnect it from the master cylinder adapter. Be careful not to spill any brake fluid.Step 14 Remove the master cylinder adapter, adjust the fluid level to the full point, and install reservoir cover.
- Vacuum Bleeding
- Step 1 Fill the master cylinder reservoir with new brake fluid and make sure it remains at least half full throughout the bleeding procedure.
- Step 2 Attach the plastic tube from the vacum bleeder to the bleeder screw of the first wheel cylinder or caliper in the bleeding sequence. If necessary, use one of the adapters provided with the vacuum in the catch bottle.
- Step 3 Operate the pump handle to create a partial vacuum in the catch bottle.
- Step 4 Loosen the bleeder screw approximately one-half turn. Brake fluid an air bubbles will flow into the bottle. When the fluid flow stops, tighten the bleeder screw.
- Step 5 Repeatsteps 3 and 4 until no more air bubbles emerge from the bleeder.
- Step 6 Transfer the vacuum bleeder to the bleeder screw of the next wheel cylinder or caliper in the bleeding sequence, and repeat steps 3 and 4. Continue around the vehicle in the specified order until the brakes at all four wheels have been bled.
- Gravity Bleeding
- gravity bleeding is a slow but effective method that will work on many vehicles to rid the hydraulic system of air. the process involves simply opening the bleeder and allowing the fluid to flow out.